Routers can "crash" for different reasons, but atypically due to high traffic. If you really wanted to fuck with someone you make one BGP change. Only newbs use DDoS's. (Which, Anonymous being newbs, would be their MO, but unlikely they could DDoS a connectionless resource record database)
If you go with 'router tables' being the culprit, they probably had a core router that maxed out its RAM when they added another router in place, but they had already moved a part of the network that housed DNS by the time the routers synced and RAM filled from too many BGP lists to sort. You can still ping 'hosts' (which are I am almost certain a hardware load balancer and not an actual DNS host) while the DNS traffic is going nowhere because the backend DNS services were moved. Would take a couple hours to unfuck all of that.